Pulverized-fuel furnace



I Aug. 5, 1930. A. E. DOU'GLASS 3 27 PULAVERIZED FUEL FURNACE Filed March 24, 1924 2 Sheets-Sheet 1 INVENTOR F1 57. 2. I 0 ALFRED E .Douemss.

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PULVERIZED FUEL FURNACE Filed March 24, 1924 2 Sheets-Sheet 2 INVENTOR ALFRED E. DOUGLA as.

/ ATTORNEYS Patented Aug. 5, 1930 UNITED STATES ALFRED E. DOUGLASS, OF OATASAU QUA, PENNSYLVANIA, ASSIGNOR, BY MESNE AS PATENT OFFICE" SIGNMENTS, TO FULLER LEHIGH COMPANY, A CORPORATION OF DELAWARE PULVERIZED-FUEL FURNACE Application filed March 24, 1924. Serial No. 701,608.

My invention relates generally to an improved furnace for burning pulverized fuel, and more particularly to an artificially cooled floor for such furnaces.

It is well known that low grade fuels,

which cannot be burned in stoker-fired furnaces, may be fired in a pulverized state as a mechanical gas, resulting in economies in the cost of fuel and tending toward the in conservation of the higher grades such as anthracite.

However, pulverized fuel furnaces have heretofore had the disadvantage of requiring a relatively large combustion chamber to avoid, in part, the rapid disintegration of the refractories forming the hearth or ash receiving surface caused by the long hot flame necessarily employed to permit complete combustion. This is particularly true in vertically fired furnaces in which the flame is directed downwardly toward the floor and is then allowed to reverse its direction to accelerate ignition of the entering fuel. It has been necessary to renew the refractories forming the floor at frequent intervals, even when the furnace is of extended height, which involves considerable expense in labor and materials and the losses resulting from these temporary shut-downs.

l/Vhen low grade fuels are employed large quantities of non-combustible materials are precipitated from the flame upon the hearth or ash-receiving surface. These particles are dition they are exposed to the radiant heat of the flame so that they are caused to fuse and run together as slag. Such an accumu lation of slag on the floor accelerates the disintegration thereof, and it cannot be removed without shutting down the furnace, permitting the slag layer to cool, and then chipping it away manually.

The objects of my invention are:

First, to provide a floor construction which may be maintained at a temperature below a point at which the reverberatory eflect of the flame and hot gases of combustion will cause substantial disintegration of the refractories;

at relatively high temperatures, andin ad- Second, to provide a construction whereby the effective height of the furnace may be considerably reduced without lowering the capacity'of the furnace, thus lowering the initial cost of pulverized fuel furnaces and also permitting the successful substitution of pulverized fuel firing for stoker firing in existing furnaces in which the relatively small combustion space would not accommodate along flame without immediate destruction of the refractories forming the floor of the furnace;

Third, to provide a floor construction which is readily accessible for cleaning and renewal, and from which the ash may be removed at frequent intervals in a convenient and expeditious manner;

Fourth, to provide a floor construction, of low initial cost and one which may be installed in existing furnaces without substantial modification of the original installation.

I am aware that it has been proposedheretofore to employ in pulverized fuel furnaces a supplemental hearth spaced a considerable distance above the ash pit floor of the furnace. This hearth is in closeproximity to the flames and the non-combustibles are pre cipitated upon it where they coalesce and, in a liquid or viscous state, drip through a central slot into the ash pit proper. Water pipes positioned below the supplemental hearth in the ash pit are intended to cool and solidify the dripping slag before it reaches the :ash deposit surface. This construction iselaborateand expensive and is difficult to renew. The refractories forming thehearth are exposed to the destructive actionof the flame and slag will necessarily accumulate upon this surface.

Water screens have been employed in pulverized fuel furnaces which are spaced a relatively considerable distance above the floor of the furnace. In one instance, ash is permitted to accumulate to a height above the water screen to the end that the floor will be protected by the bed of ash, and fusion of the latter above the screen be avoidedfby the cooling effect of the water screen, but such installations are objectionable in view of the corrosive action of the acid-constituents of the hot ash both above and below the screen, the necessity of frequent renewals, the close attention necessary to prevent fusion of the ash at the top of the bed and the practical difliculties involved in cleaning and operating the furnace.

In a second construction of this type which differs from the first by keeping the ash below the level of the water screen, the screen is intendedto cool the ash below the temperature of fusion beforethe ash particles are deposited upon the floor. No direct means for cooling the floor is provided in this system.

The screen is subject to the radiant heat from the surface of the bed of ash below it, and the relatively large quantities of heat thus absorbed cause the pipes to buckle and sag. The accumulation of ash and slag upon the screen and the. position of the screen make ash and slag removal diflicult and renewals inconvenient and expensive. Further, the combustionchamber cannot be appreciably reducedin size, and the effect of the cool zone upon the combustible constituents passing through this portion of the furnace results in substantial losses of fuel which passes through the boiler and into the stack before co nbustio nhas been completed.

. According tothe -preferred form ofmy invention, a pluralityofwater-tubes are positioned flush with or partially embedded in the ashreceiving fioor and are separated by refractories forming channels whereby the upper surfaces of the tubes and refractories 7 lie in substantially the same plane. It is also preferred to position the tubes at an angle of 90 degrees from the clean-out doors in order that the ash may be moved in the direction of the length of the tubes to make cleaning more convenientand to prevent injury to the refractories by the tools used in cleaning. The tubes may be connected to headers in groups to form units, whereby a single unit may be removed for repair or renewal. e v

The water tubespreferably may be made a part of the circulatory system of the boiler in order to insure a circulation of water therethrough and in order to employ the heat absorbed most advantageously, but it is to be'understoodthat. the feed water maybe circulated through the tubes as an alternative construction.

A preferred form of my invention is illustrated in the accompanying drawings in which like reference characters refer to like parts and in which: I V

Fig. 1 is a sectionalplan view of a furnace, showing my improvedfloor construction. I i i Fig. 2 is a sectional elevation on line A A of Fig. 1, showing the position of the Water tubes with relation to the walls and floorof thefurnace. r

Fig. 3 is a sectional elevation on line BB of Figs. 1 and 2.

The three figures of the drawings illustrate the lower portion of a furnace showing my improved construction. The burners, the boiler, etc, are not shown as they form no part of the present invention, and, although the floor construction is intended as an improvement in pulverized fuel furnaces, it is obviously applicable to furnaces other than boiler furnaces without departing-from the spirit oftheinvention.

The floor or ash receiving surface is indicated at lO, and is surrounded by the front wall 11, side walls 12 and 13, and a back wall14. l V

The floor. 10 is provided with a plurality of parallel channels 15' disposed at right angles to the front'wall 11 andthe back wall 14. The channels 15 maybe formed between rows of refractory brick, as at 16, or by means of specially designed tiling having channels provided for this purpose. v

Apluralityof water tubes 17 are positioned in the channels 15 and preferably in contact with the bot-tom and side walls of the channels, although it; will beapparent that the tubes may be slightly'spaced from the side walls when refractories of the proper dimension cannot be'obtained conveniently. The upper exposed surfaces of the refractory tiling or fire brick 16 forming the channels '15 are preferably; formed to lie in the same plane as the upper surfaces of the tubes 17,

whereby the combined surfaces of the water tubes and refractories 16 form a substantially smooth floor or ash receiving surface.

The water tubes 17 are preferably directed through the front wall 11 and the rear wall 14, through 'pipesleeves 18 and 19, and are then directed downwardly as at 20,21 and terminate in headers, generally indicated at 22; and 23, preferably slightly spaced from the front and back walls of the furnace.

Although it is apparent that all of the water tubes 17 could terminate in'a single header positioned on each side of the fur nace, as an added improvement I prefer to employ a plurality of separatev headers on each side of the furnace. In the example shown in. the drawings fourheaders, 24, 25, 26 and 27 are shown positioned along the front wall ,of the furnace, and four complementary headers 28, 29, 30 and31 are located in a likeposition along the back wall. The tubes 17 are connected in groupsto pairs of heads ers, as for instance, in groups of four, as illustrated. I have thus provided a plurality of independent-groupsor unitary cooling elements. 1 I I V.

Iffor eXample,.the-front,of the'furnaceis taken as the inlet side, I prefer to provide a plurality ofwater inlet tubes 32; connected to each header, the preferred number of such tubes being about half the number oftubes 17 in each unit. The tubes 32 are preferably disposed half way between each pair of tubes 17 fed thereby, in order to insure an equal distribution of cooling water to each tube 17. Outlet tubes 33 for the cooling water are connected to each of the complementary headers 28-31 in the samemanner. The direction of flow of the cooling medium is in,- dicated by the arrows in Figs. 1 and 2.

in order that the heat absorbed by the cooling water may be usefully employed, the inlet tubes 32 and outlet tubes 33 may be connected to the boiler in the usual manner whereby the cooling units will form a part of the circulatory system of the boiler.

A plurality of ash removal ports or doors 4 are provided in the front wall 11 of the furnace immediately above the floor, and similar ports or doors are provided in the back wall 14.

The cooling efiect of the water tubes 17 is such that the heat is absorbed rapidly from the refractories and slag cannot, therefore, adhere either to the floor or to the water tubes.

Ash may be removed conveniently and at frequent intervals from the furnace floor. The tools used in cleaning the floor move lengthwise of and rest partially upon the water tubes, thereby further avoiding injury to the refractories in the process of cleaning In the accompanying drawings, four groups or units of headers and tubes have been illustrated, but it is apparent that the number will be increased or decreased, depending upon the capacity of the furnace, the size of the furnace and the distance of the pulverized-fuel burners above the floor. The number of tubes in each. unit or group may be varied, but it is preferred to provide comparatively few tubes in each group in order that a complete circulation of water may be obtained, and to avoid the liability of steam and dry spots which may result if large units are employed and which would tend to destroy the function of the cooling units. WVhile I have described my invention as employing water as a cooling medium, it is to be understood that the use of another medium, such as air, is contemplated to be withinthe spirit and scope of the invention.

The preferred location of the headers is, as illustrated, below the level of the floor, in order that the ash removal doors will be readily accessible, but the headers may be positioned in any other suitable location to be adaptable to modified forms of furnaces.

It will be apparent from the foregoing description, that by my invention the refractories forming the floor, are rapidly cooled by the closely adjacent water tubes 17, to a temperature at which they will not suffer rapid disintegration from the reverberatory effect of the flame and hot gases of combustion. The sides and bottoms of the channels 15 are substantially in direct contact with the cooling means, and heat is rapidly transferred, and, accordingly, ash will not fuse and slag will not accumulate upon the floor to any appreciable extent in a form in which it cannot be easily removed in the usual operation of cleaning. The unitary and independent construction of the cooling devices makes renewals convenient and inexpensive, and individual units may be removedor taken out of operation in an expeditious manner. Due to the artificial cooling of the refractory floor, the effective height of the furnace may be considerably reduced, thereby lowering the initial cost of the furnace, and permitting the successful conversion of existing stoker-fired furnaces to pulverized-fuel firing with a minimum of expense.

I claim:

1. In a furnace construction, a refractory floor, provided with a plurality of parallel upwardly opening channels, water-tubes positioned in said channels to provide a cooling means for said channels and floor, ash removal ports in opposite walls ofsaid furnace positioned above the level of the tubes, said tubes being disposed at right angles to said opposite walls, whereby ash may be removed lengthwise of the tubes.

2. In a furnace construction, a refractory floor provided with a plurality of parallel upwardly opening channels, water-tubes positioned in said channels, the upper surfaces of said tubes lying in substantially the same plane as the upper edges of said channeled portion, to provide a substantially plane ash deposit surface, cleanout doors provided in opposite walls of the furnace and disposed above said ash deposit surface, said tubes being disposed at right angles to the plane of said opposite walls, whereby ash may be removed longitudinally of said water-tubes.

3. In a furnace, a refractory floor provided with a plurality of parallel upwardly opening channels, watertubes positioned in said channels, ash removal doors. provided in opposite walls of said furnace, said tubes being disposed beneath and at right angles to the plane of said ash removal doors, extending through said opposite walls directed downwardly to headers located exteriorly of said opposite walls, water inlet means for one of said headers and water out-let means for the other of said headers, whereby cooling water may be circulated across said floor to cool the refractories forming the same.

4. In a furnace, a refractory floor provided with a plurality of parallel upwardly opening channels, water-tubes positioned in said channels, ash removal doors provided in opposite walls of said furnace, said water tubes, disposed beneath and at right angles to the plane of said ash removal doors, extending through said opposite walls, a plurality. of headers on eachside of the furnace adjacent water tubes being connected to pairs of said headers to provide a plurality of parallel independent cooling units for the floor of said furnace, separate water inlet means connected toeach header on one side of the furnace, and separate water out-let means connected to each header on the other side of said furnace.

5. In a furnace construction, a combustion chamber having defining walls and a floor, the floor being made of refractory material constructed to provide a plurality of closely spaced, open top channels, a tube in each channel lying in contact with the bottom and side walls thereof and with its top substantially in the plane of the top of the channelled portion of the refractory material and means for circulating a cooling medium through the said tubes.

6. In a furnace construction, a combustion chamber having defining walls and a floor, the floor being made of refractory material constructed to provide a plurality of closely spaced, open top channels extending across the floor, a tube in each channel lying in contact with the bottom and side walls thereof and with its top substantially in the plane of the top of the channeled portion of the refractory material, these tubes extending through openings in the opposite walls of the furnace to which the channels lead, headers connecting the ends of groups of tubes outside the furnace walls, and means for supplying a cooling medium to the headers at one side of the combustion chamber and for withdrawing the medium from the headers at the opposite side of the combustion chamber.

7. In a furnace construction, a combustion chamber comprising side walls and a floor,

the floor being made of refractory material constructed to provide a plurality of closely spaced, open topchannels extending across the floor between opposite side walls thereof,

4 tubes in the channels extending through said opposite walls, each tube lying in contact with the bottom and side walls of its channel and with its top substantially in the plane of the top of the channelled portion of the refractory material, headers connecting groups of tubes at opposite sides of the furnace, these headers lying below the level of the floor thereof, means for supplying a cooling medium to the headers at one side'of the combustion chamber and withdrawing it" from headers at the opposite side, and cleanout doors disposed in the side walls of the furnace through which the tubes extend, these doors being positioned slightly above the upper surfaces of the tubes.

8. In a furnace construction, a combustion chamber comprising side walls and an ashreceiving floor, the floor being made. up of refractory material constructed to provide a plurality of parallel open top channels of square section, tubes in the channels, each tube lying in contact with the bottom and side walls thereof and with its top substantially in the plane of the top of the channelled portion of the refractory material, the tubes extending through opposite side walls of the chamber, and means for circulating a cooling medium through the tubes.

9. In a furnace construction, a combustion chamber comprising side walls and a floor, the floor being made of refractory material constructed to provide a plurality of closely spaced open top channels of square section, tubes in the channels lying in contact with the bottom and side walls thereof, the tops of the tubes lying substantially in the plane of the top of the channeled portion of the refractory material, the tubes extending through opposite side walls of the furnace, and means connected to the tubes outside the furnace for supplying a cooling medium thereto which flows through the portions of the tubes exposed in the combustion chamber.

10. In a furnace construction, a combustion chamber comprising side walls and an ash-receiving floor, this floor being made up of refractory material constructed to provide a plurality of parallel open top channels of square section, the channels extending between opposite walls of the furnace, tubes in the channels lying substantially in contact with the bottom and side walls thereof, the tops of the tubes lying in a plane substantially flush with the top of the channeled portion of the refractory material, the tubes extending through the side walls, headers connecting the projecting ends of groups of tubes and extending parallel to the side walls of the chamber, connections for supplying a cooling medium to the headers at one side of the chamber, and outlet connections from the headers at the opposite sides, and cleanout doors in the walls of the chamber through which the tubes project, these doors lying above the plane of the headers and of the floor.

In testimony whereof I afix my signature. ALFRED E. DOUGLASS. 

